An understanding of cardiac specific transcription is fundamental to an eventual understanding of the molecular mechanisms that govern cardiac determination, differentiation and pathology because the earliest events in these processes are known to involve specific gene activation. We have been studying the cis and trans regulation of the promoter of the cardiac troponin T (cTNT) gene. Cardiac specific expression of cTNT requires two disparate elements in cis. One of these is a promoter element, consisting of two conserved M-CAT motifs. We have cloned the factors binding to the M-CAT elements and shown them to be isoforms to TEF-1, a member of the TEA domain family. The other element,known as the cardiac element, resides upstream and consists of GC-rich and AT-rich sub-elements. The factor binding to this element have not et been unequivocally determined but one is likely to be a cardiac form of MEF-2, a member of the MADS box family of transcriptional activators. Both TEF-1 and MEF-2 exist as multiple isoforms in cardiac muscle cells. The proposed experiments will the identify active forms of factors that regulate the cTNT promoter and the molecular details of their interactions in formation of the transcription initiation complex. From the proposed studies we expect to gain a detailed picture of the mechanism of transcriptional activation of the cTNT promoter. The results of these studies should be applicable to other cardiac promoters because both TEF-1 and/or MEF-2-like proteins have been implicated in the regulation of all known cardiac promoters to date. Moreover, the interactions of these factors with other regulatory components of the cardiac cell, such as those controlling cell cycle and cytoplasmic signalling, should yield an overall picture of the role of transcription factors in establishing and maintaining the differentiation state of cardiac myocytes. This information may lead to a general understanding of how these cells alter their differentiation state pathologically, for example during cardiomyocyte hypertrophy.